The present invention relates to the class of electrical devices which are generally known as ground fault circuit interrupters. More specifically, the invention relates to novel features of circuitry which interrupt the lines between a source of electrical power and a load in response to an imbalance of predetermined magnitude in current flow through the current-carrying wires connected between the source and load.
The possibility of injury and/or damage which is inherent in the operation of any electrical system of significant magnitude has led to the provision of various protective devices. Among these are the class of electrical apparatus which has come to be known as ground fault circuit interrupters (GFCI). In general, such apparatus senses and/or responds to a condition in a line carrying electrical current which indicates a presently or imminently dangerous condition, such as the presence of a current path other than the intended path of normal operation. Response to the sensed dangerous condition may be in the form of alarm actuation and/or opening the line (interrupting the circuit) between the source of power and the load.
The present invention is concerned with the type of GFCI which utilizes a differential transformer to sense an imbalance of current flow in the conductors of a distribution system and provide a signal in response to the imbalance which actuates a relay to remove power from the load. The general object of the invention is to provide an electrical circuit for such a GFCI having novel and improved features.
A more specific object is to provide a GFCI including a relay coil in a circuit configuration having lowered total power consumption, thereby producing less heat, than similar prior circuits.
A further object is to provide novel and improved circuit mean operable to actuate an electro-mechanical relay from a source of pulsating DC voltage in an improved manner, reducing the possibility of contact chatter or welding.
Another object is to provide a GFCI having a relay coil receiving an input from a transistor and a novel circuit arrangement which not only protects the transistor upon removal of the coil input signal, but also provides more rapid field collapse and does not increase contact opening time.
An additional object and important advantage of the invention is to provide a GFCI with novel circuit features providing an optimum fail-safe capability: that is, if the GFCI fails, malfunctions or is defective in any of a variety of ways, the circuit between source and load either opens in response to such failure or is already open and cannot be closed, thereby not defeating the desired protection.
All of the foregoing features and advantages are incorporated in a GFCI which also provides protection in the event of a grounded or open neutral line, as well as circuit testing and resetting capabilities.
Other objects will in part be obvious and will in part appear hereinafter.